Calcium oxide dispersion liquid and process for production thereof

ABSTRACT

A calcium oxide dispersion liquid contains calcium oxide fine particles having a median particle diameter (volume basis) of 1 to 200 nm and a maximum particle diameter of 10 to 1,000 nm, and an organic dispersion medium. The calcium oxide dispersion liquid is produced by filling calcium oxide fine particles, an organic dispersion medium, and beads 5 to 200 μm in diameter into a container, and stirring these materials. Therefore, the calcium oxide having a small particle diameter and a high purity is homogeneously dispersed in the calcium oxide dispersion liquid.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is an application filed under 35 U.S.C. §111 (a)claiming benefit pursuant to 35 U.S.C. §119(e) (1) of the filing date ofProvisional Application 60/564,973 filed Apr. 26, 2004 pursuant to 35U.S.C. §111(b).

FIELD OF THE INVENTION

The present invention relates to a dispersion liquid of calcium oxidefine particles, and a process for production thereof. Specifically, thepresent invention relates to a high-concentration dispersion liquid ofcalcium oxide fine particles which have a small particle diameter andare homogeneously dispersed, and a process for production thereof.

BACKGROUND OF THE INVENTION

Calcium oxide is highly hygroscopic, and is useful as a moistureabsorbent and a dehydrating agent. The use as a moisture absorbent or adehydrating agent requires calcium oxide to be highly active. Therefore,it is desirable that the particles thereof be nanoparticles having alarge surface area, and that the particles contain as little calciumhydroxide and calcium carbonate as possible that are inactive indehydration. Furthermore, calcium oxide manufactured on a nanoscale cangive a paste having optical transparency. In addition, from theviewpoint of handling, calcium oxide is desirably provided in the formof a homogeneous dispersion liquid.

Calcium oxide has been produced by thermally decomposing limestone atabout 1200° C. However, due to the high temperature, the particlesthereof become enlarged in diameter and are sintered together to form ahard material. Accordingly, it takes a lot of energy and time topulverize the resulting material into nanoparticles. However, calciumoxide for use as a moisture absorbent or a dehydrating agent should beprevented from absorbing moisture during production, and thereforetime-consuming treatment is inappropriate. Furthermore, conventionalsynthetic methods of calcium oxide have difficulty in producing adispersion liquid containing no inactive substances from particleshaving an extremely small particle diameter. In addition, the smallerthe particle diameter of calcium oxide, the higher the slurry viscosity.Accordingly, it has been impossible to produce a high concentrationslurry of calcium oxide nanoparticles by conventional techniques.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide a calcium oxidedispersion liquid in which highly purified calcium oxide having a smallparticle diameter is homogeneously dispersed, and a process forproduction thereof.

The inventors have developed a synthetic method of metal oxidenanoparticles by gas phase oxidation of an organometallic β-diketonecomplex. This method enables synthesis of primary particles having amedian particle diameter of not more than 200 nm. Because the particlesobtained are in the form of aggregates, they are pulverized by use of 50μm fine beads and are dispersed in an optimum dispersion medium (alcoholor the like) to give a homogeneous dispersion liquid of calcium oxidefine particles. It has been revealed that the calcium oxide particlesexhibit completely different dispersibility depending on the type of thedispersion medium. It has also been found that selection of the solventin view of dipole moment and viscosity, or optimum mixing of theselected solvents leads to a stable dispersion liquid of calcium oxidenanoparticles. It has also been found that short-time treatment in aninert gas atmosphere can inhibit inactivation of calcium oxide.

The present invention basically pertains to the following [1] to [22].

[1] A calcium oxide dispersion liquid comprises:

calcium oxide fine particles having a median particle diameter (volumebasis) of 1 to 200 nm and a maximum particle diameter of 10 to 1,000 nm;and

an organic dispersion medium.

[2] The calcium oxide dispersion liquid has a calcium oxideconcentration of 10 to 50% by mass.

[3] The calcium oxide dispersion liquid is obtained by using the organicdispersion medium which has a water content of less than 1,000 ppm (bymass) as a raw material.

[4] In the calcium oxide dispersion liquid, the calcium oxide fineparticles are obtained by vaporizing a calcium complex, and thenoxidizing the resultant gaseous calcium complex in gas phase.

[5] In the calcium oxide dispersion liquid, the calcium oxide fineparticles are obtained by vaporizing a calcium complex, oxidizing theresultant gaseous calcium complex in gas phase to obtain calcium oxidefine particles, and then subjecting the fine particles to bakingtreatment.

[6] In the calcium oxide dispersion liquid, the calcium complex is acomplex of calcium and a β-diketone compound.

[7] In the calcium oxide dispersion liquid, the calcium oxide fineparticles have a calcium hydroxide content of less than 5% by mass and acalcium carbonate content of less than 1% by mass.

[8] In the calcium oxide dispersion liquid, the organic dispersionmedium is at least one medium selected from the group consisting ofalcohol, nitrile compound, aamide compound and polyol derivative.

[9] In the calcium oxide dispersion liquid, the alcohol has 3 or morecarbon atoms.

[10] In the calcium oxide dispersion liquid, the organic dispersionmedium is diol derivative.

[11] In the calcium oxide dispersion liquid, the organic dispersionmedium is at least one medium selected from the group consisting ofacetonitrile, 1-butanol, 1-hexanol and 1-methoxy-2-propanol.

[12] In the calcium oxide dispersion liquid, the organic dispersionmedium is a mixed dispersion medium.

[13] In the calcium oxide dispersion liquid, the organic dispersionmedium is at least one medium selected from the group consisting of anitrile compound/alcohol mixed dispersion medium, an aromaticcompound/alcohol mixed dispersion medium, an aromatic compound/aminecompound mixed dispersion medium, an ester/alcohol mixed dispersionmedium, an amide compound/alcohol mixed dispersion medium, an aromaticcompound/nitrile compound mixed dispersion medium and a polyolderivative/amine compound mixed dispersion medium.

[14] In the calcium oxide dispersion liquid, the mixed dispersion mediumis at least one medium selected from the group consisting of atoluene/alcohol mixed dispersion medium, a butyl acetate/alcohol mixeddispersion medium, an N,N-dimethylacetamide/alcohol mixed dispersionmedium, a diethylene glycol dimethyl ether/monoethanolamine mixeddispersion medium, a diethylene glycol dimethyl ether/diethanolaminemixed dispersion medium and a diethylene glycol dimethylether/triethanolamine mixed dispersion medium.

[15] The calcium oxide dispersion liquid contains a dispersant.

[16] In the calcium oxide dispersion liquid, the dispersant is at leastone compound selected from nonionic surfactants.

[17] In the calcium oxide dispersion liquid, the nonionic surfactant hasa hydroxyl group.

[18] In the calcium oxide dispersion liquid, the nonionic surfactant isan adduct of glycerin with polypropylene oxide.

[19] In the calcium oxide dispersion liquid, the organic dispersionmedium has a viscosity of not more than 3.0 mPa·s (20° C.).

[20] A process for producing the calcium oxide dispersion liquidcomprises the steps of:

filling calcium oxide fine particles, an organic dispersion medium, andbeads having a diameter of 5 to 200 μm into a container; and

stirring these materials.

[21] In the process, the stirring is carried out in an atmosphere of aninert gas having a water content of not more than 10 ppm (by mol).

[22] In the process, the organic dispersion medium to be filled in thecontainer has a water content of less than 1,000 ppm (by mass).

EFFECTS OF THE INVENTION

The calcium oxide dispersion liquid according to the present inventionis very useful as a moisture absorbent and a dehydrating agent becauseit hardly contains any calcium hydroxide and calcium carbonate which areinactive in dehydration, namely, the calcium oxide contained is highlypurified. In addition, the dispersion liquid has high performance as amoisture absorbent since the calcium oxide particles are fine and have alarge surface area. Further, application of the dispersion liquid givesa film having high transparency. Moreover, the dispersion liquid is veryadvantageous in terms of cost because the calcium oxide fine particlescan be dispersed in high concentration. Owing to these characteristics,the calcium oxide dispersion liquid of the present invention can beapplied to precision mechanical equipment and electronic materials(organic EL, ELD and the like).

The process for production of a calcium oxide dispersion liquidaccording to the present invention permits efficient production of thecalcium oxide dispersion liquid having the above-described excellentproperties.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an embodiment of a production apparatus used for producingthe calcium oxide fine particles according to the present invention; and

FIG. 2 is an electron microscope photograph of the calcium oxide fineparticles obtained in Production Example 1.

DESCRIPTION OF SYMBOLS

-   1 . . . Oxidizing substance-   2 . . . Solution-   3 . . . Mass flow controller-   4 . . . Metering pump-   5 . . . Preheater-   6 . . . vaporizer-   7 . . . Tubular heating furnace-   8 . . . Collector

PREFERRED EMBODIMENTS OF THE INVENTION

The calcium oxide dispersion liquid and process for production thereofaccording to the present invention are described in detail below.

Calcium Oxide Dispersion Liquid

The calcium oxide dispersion liquid of the present invention comprisescalcium oxide fine particles and an organic dispersion medium.

The calcium oxide fine particles have a median particle diameter(particle diameter at which the volume accumulation rate (massaccumulation rate shows the same value when the density of particles isconstant) is 50%: D₅₀) of 1 to 200 nm, preferably 5 to 150 nm, and morepreferably 10 to 100 nm, and have a maximum particle diameter of 10 to1,000 nm, preferably 15 to 500 nm, more preferably 20 to 250 nm, andstill more preferably 50 to 150 nm. Unfavorably, when the particlediameter is larger, problems arise such that fine processing isimpossible and optical transparency is lowered, and the surface areadecreases to reduce moisture absorption efficiency.

The median particle diameter and maximum particle diameter of thecalcium oxide in the calcium oxide dispersion liquid are measured bylaser Doppler method, optionally after the dispersion liquid is dilutedwith the same organic dispersion medium as used in the liquid. Themeasurements of the median particle diameter and maximum particlediameter can be carried out, for example, by Nanotrac UPA-EX150 orMicrotrac UPA-150 manufactured by NIKKISO CO., LTD.

The organic dispersion medium is not particularly limited. Preferableexamples thereof include organic solvents such as alcohols, nitrilecompounds, amide compounds and polyol derivatives, mixtures of thesesolvents, aromatic compound/alcohol mixed dispersion media, aromaticcompound/amine compound mixed dispersion media, ester/alcohol mixeddispersion media, aromatic compound/nitrile compound mixed dispersionmedia and diol derivative/amine compound mixed dispersion media.Furthermore, when an aggregation-inhibiting effect by electrostaticrepulsion is desired, a protic solvent is preferable.

Examples of the alcohols include those having 1 to 10 carbon atoms suchas methanol, ethanol, propanol, isopropanol, butanol, pentanol, hexanol,heptanol, octanol, cyclopentanol and cyclohexanol. In particular, thealcohols having 3 or more carbon atoms are preferable because of thehigh reaggregation-inhibiting effect and low hygroscopicity. Of thesealcohols, 1-butanol is particularly preferable.

The nitrile compounds are organic solvents having a cyano group (—CN).Examples thereof include nitrile compounds having 1 to 10 carbon atomssuch as acetonitrile, succinonitrile, propionitrile, butyronitrile,acrylonitrile, adiponitrile and benzonitrile. Of these compounds,acetonitrile is particularly preferable.

The amide compounds are organic solvents having an amide group. Examplesthereof include formamide, N-methylformamide, N,N-dimethylformamide,N,N-diethylformamide, acetamide, N-methylacetamide,N,N-dimethylacetamide, N,N-diethylacetamide and N-methylpropionamide.

The polyol derivatives are preferably polyol monoethers, polyoldiethers, polyol monoesters and polyol diesters.

Examples of the polyol derivatives include diol derivatives such as1-methoxy-2-propanol, 1-ethoxy-2-propanol, 1-butoxy-2-propanol,diethylene glycol ethyl methyl ether, diethylene glycol diethyl ether,diethylene glycol dibutyl ether, diethylene glycol dimethyl ether,diethylene glycol monoethyl ether, diethylene glycol monoethyl etheracetate, diethylene glycol monobutyl ether, diethylene glycol monobutylether acetate, diethylene glycol monomethyl ether, ethylene glycoldiacetate, ethylene glycol diethyl ether, ethylene glycol dibutyl ether,ethylene glycol dimethyl ether, ethylene glycol monoacetate, ethyleneglycol monoisopropyl ether, ethylene glycol monoethyl ether, ethyleneglycol monoethyl ether acetate, ethylene glycol monobutyl ether,ethylene glycol monobutyl ether acetate, ethylene glycol monohexylether, ethylene glycol monomethyl ether, ethylene glycol monomethylether acetate and ethylene glycol monomethoxymethyl ether; andderivatives of polyol having 3 or more hydroxyl groups, such as glycerolmonoacetate, glycerol diacetate, glycerol triacetate and glyceroldialkyl ether (for example, 1,2-dimethyl glycerol, 1,3-dimethylglycerol, 1,3-diethyl glycerol). Of these derivatives,1-methoxy-2-propanol is particularly preferable.

The organic dispersion medium used for the calcium oxide dispersionliquid of the present invention may be a mixed dispersion mediumconsisting of two or more kinds of the organic dispersion media. Themixed dispersion medium permits production of a higher concentrationcalcium oxide dispersion liquid. Examples of the preferable mixeddispersion media are described below.

Nitrile Compound/Alcohol Mixed Dispersion Media

Examples of the nitrile compounds and alcohols used for the mixeddispersion media are as described above. Preferred combinations includeacetonitrile and the alcohol (particularly 1-butanol or 1-hexanol). Themixed dispersion medium preferably has an alcohol concentration of 0.005to 50% (by mass), more preferably 0.01 to 10%, and most preferably 0.01to 0.5%.

The mixed dispersion medium may contain a third solvent component.Examples of the third components include amine compounds, such asmonoethanolamine, diethanolamine, triethanolamine, monoethylamine,diethylamine, triethylamine and ethylenediamine.

Aromatic Compound/Alcohol Mixed Dispersion Media

Examples of the aromatic compounds include benzene, toluene, xylene andethylbenzene. The alcohols include those described above. Preferredcombinations include toluene/1-hexanol, xylene/1-hexanol andethylbenzene/1-hexanol.

The mixed dispersion medium preferably has an alcohol concentration of0.005 to 50% (by mass), more preferably 0.01 to 10%, and most preferably0.01 to 0.5%. The mixed dispersion medium may contain a third component.Examples of the third components include the above-described aminecompounds.

Aromatic Compound/Amine Compound Mixed Dispersion Media

The aforementioned aromatic compounds can be used herein. Examples ofthe amine compounds include monoethanolamine, diethanolamine,triethanolamine, monoethylamine, diethylamine, triethylamine andethylenediamine. Preferred combinations include xylene/monoethanolamine.The mixed dispersion medium preferably has an amine compoundconcentration of 0.005 to 50% (by mass), more preferably 0.01 to 10%,and most preferably 0.01 to 5%.

Ester/Alcohol Mixed Dispersion Media

Preferred examples of the esters include ethyl formate, propyl formate,butyl formate, methyl acetate, ethyl acetate, propyl acetate, butylacetate, pentyl acetate, methyl pivalate and ethyl pivalate. Thealcohols are as described above. Preferred combinations include butylacetate/1-butanol, butyl acetate/1-hexanol and alkyl pivalate/1-hexanol.

The mixed dispersion medium may contain a third component. Examples ofthe third components include the above-described amine compounds. Themixed dispersion medium preferably has an alcohol concentration of 0.005to 50% (by mass), more preferably 0.01 to 10%, and most preferably 0.01to 0.5%.

Amide Compound/Alcohol Mixed Dispersion Media

The amide compounds and alcohols are as described hereinabove. Preferredcombinations include N,N-dimethylformamide/alcohol (particularly1-butanol or 1-hexanol), and N,N-dimethylacetamide/alcohol (particularly1-butanol or 1-hexanol). The mixed dispersion medium may contain a thirdcomponent. Examples of the third components include amine compounds. Themixed dispersion medium preferably has an alcohol concentration of 0.005to 50% (by mass), more preferably 0.01 to 10%, and most preferably 0.01to 0.5%.

Aromatic Compound/Nitrile Compound Mixed Dispersion Media

The aromatic compounds and nitrile compounds are as describedhereinabove. The mixed dispersion medium may contain a third component.Examples of the third components include amine compounds. The mixeddispersion medium preferably has a nitrile compound concentration of0.005 to 50% (by mass), more preferably 0.01 to 10%, and most preferably0.01 to 0.5%.

Polyol Derivative/Amine Compound Mixed Dispersion Media

The aforementioned polyol derivatives and amine compounds can be usedherein. Preferred combinations include diethylene glycol dimethylether/amine compound (particularly, hydroxyl-containing amine compoundssuch as monoethanolamine, diethanolamine and triethanolamine). The mixeddispersion medium may contain a third component.

The mixed dispersion medium preferably has an amine compoundconcentration of 0.005 to 50% (by mass), more preferably 0.01 to 10%,and still more preferably 0.01 to 5%.

The calcium oxide dispersion liquid may contain a dispersant. Thedispersant provides enhanced fluidity and stability, and therefore thediameter of dispersed particles can be reduced. The dispersant is notparticularly limited. Nonionic surfactants, particularly thosecontaining a hydroxyl group, are suitable.

The nonionic surfactants include ether surfactants such aspolyoxyethylene alkyl ether, polyoxyethylene secondary alcohol ether,polyoxyethylene alkylphenyl ether, polyoxyethylene, polyoxypropyleneblock copolymers, polyoxyethylene polyoxypropylene alkyl ether andadduct of glycerin with polypropylene oxide; and ester ether surfactantssuch as polyoxyethylene glycerin fatty acid ester, polyoxyethylenecastor oil and hardened castor oil, and polyoxyethylene sorbitan fattyacid ester. Of these, adduct of glycerin with polypropylene oxide isparticularly preferred.

The amount of dispersant is dependent on the compound selected, andpreferably ranges from 0.1 to 10% (by mass) relative to calcium oxide.

The dispersant may be added to the dispersion medium before or aftercalcium oxide is dispersed in the dispersion medium with a bead mill.Preferably, the addition is performed prior to dispersing with a beadmill, in which case the fluidity and stability are further enhanced.

The organic dispersion medium used as a raw material in the presentinvention preferably has a low water content before calcium oxide isdispersed, generally less than 1,000 ppm (by mass), preferably 500 ppm(by mass), more preferably less than 100 ppm (by mass), still morepreferably less than 10 ppm (by mass), and still more preferably lessthan 5 ppm (by mass). The calcium oxide dispersion liquid having a watercontent in the above range is preferable because there is no increase ofcalcium hydroxide content and problems such as coloration and viscosityincrease do not occur. The organic dispersion medium having this lowwater content can be obtained by dehydration with molecular sieves orcalcium oxide.

The water content of the organic dispersion medium is measured using acoulometric Karl Fischer moisture titrator suchas CA-06 manufactured byMitsubishi Chemical Corporation.

The calcium oxide dispersion liquid according to the present inventionpreferably has a calcium oxide concentration of 10 to 50% by mass, morepreferably 20 to 50% by mass, still more preferably 25 to 50% by mass,and most preferably 30 to 50% by mass. When the calcium oxideconcentration is lower than the above-described range, a large amount ofthe dispersion medium is required for preparing the calcium oxidedispersion liquid in order to obtain moisture absorption effect. Whenthe calcium oxide concentration is higher than the above-describedrange, the dispersion liquid has an increased viscosity to causedifficult handling. The calcium oxide concentration in the dispersionliquid can be calculated from the amounts of the raw materials to beused when preparing the dispersion liquid, and can be determined by thefollowing method (a) or (b) after preparation of the dispersion liquid.

(a) The dispersion medium is removed from the dispersion liquid by amethod such that the dispersion medium is evaporated off under reducedpressure by a rotary evaporator or such that the dispersion liquid isheated to 200° C. in the atmosphere. The resulting residue is dissolvedin an acid such as hydrochloric or sulfuric acid, and the solution isdiluted with pure water, followed by measuring the calcium concentrationusing an atomic absorption measuring apparatus (for example, atomicabsorption spectrophotometer SAS-7500A manufactured by Seiko InstrumentsInc.) or an ICP measuring apparatus (for example, ICP mass spectrometerSPQ-9000 manufactured by Seiko Instruments Inc.) to determine thecalcium oxide concentration in the dispersion liquid by calculation.

(b) The dispersion medium is removed from the dispersion liquid asdescribed in the method (a). The resulting residue is heated to 1,000°C. under atmosphere pressure using a thermobalance apparatus (forexample, TG/DTA6200 model manufactured by Seiko Instruments Inc.) toafford residual calcium oxide. The weight of the residual calcium oxideis measured to calculate the calcium oxide concentration in thedispersion liquid.

In the calcium oxide dispersion liquid according to the presentinvention, the calcium oxide fine particles have a calcium hydroxidecontent of less than 5% by mass, and preferably less than 1% by mass,and have a calcium carbonate content of less than 1% by mass, andpreferably less than 0.5% by mass. The calcium oxide dispersion liquidcontaining calcium hydroxide and calcium carbonate in theabove-described range has high performance as a moisture absorbent and adehydrating agent because of substantial absence of calcium hydroxideand calcium carbonate inactive in dehydration.

The calcium hydroxide content and calcium carbonate content are measuredby a thermobalance apparatus. The calcium hydroxide content iscalculated from weight reduction that is caused by dehydration ofcalcium hydroxide occurring at around 300° C. The calcium carbonatecontent is calculated from weight reduction that is caused bydecarboxylation of calcium carbonate taking place at about 700° C.

The viscosity of the dispersion medium is preferably low in order toproduce the dispersion liquid of calcium oxide fine particles in highconcentration. The viscosity is preferably not more than 3.0 mPa·s (20°C.), and still preferably not more than 1.0 mPa·s (20° C.). In the caseof the mixed dispersion medium, the viscosity of the mixed dispersionmedium preferably falls in the above-described range.

Process for Producing Calcium Oxide Dispersion Liquid

It is usually difficult to further pulverize micrometer or larger sizedparticles of calcium oxide to a median particle diameter of not morethan 200 nm. Accordingly, it is preferable that the calcium oxideparticles to be dispersed in the dispersion medium have a medianparticle diameter of not more than 200 nm.

The calcium oxide fine particles having this particle diameter can beobtained, for example, by a method in which a calcium complex such as acomplex of calcium and a β-diketone compound (β-diketone/calciumcomplex) or a calcium alkoxide is vaporized, and the resulting gaseouscalcium complex is combusted in the presence of an oxidizing substance.

Alternatively, the calcium oxide fine particles can be obtained by amethod in which a solution of a β-diketone/calcium complex (in a solventsuch as an alcohol) is vaporized, the vapor containing the gaseousβ-diketone/calcium complex is mixed with a gaseous oxidizing substance(air or the like), and the resulting mixture is heated to combust thegaseous β-diketone/calcium complex.

Preferred β-diketone/calcium complexes for use in the present inventioninclude calcium complexes of 2,2,6,6-tetramethylheptane-3,5-dione(DPM.H), 2,6-dimethyl-3,5-heptanedione (DMHD.H) and 2,4-pentanedione(acac.H). Specific examples include Ca(DPM)₂, Ca(DMHD)₂, Ca (acac)₂ andn-hydrates thereof (n is a number of 1 or more) As used herein, “acac”or the like means a ligand produced by elimination of H⁺ from acac.H orthe like.

Preferred examples of the calcium alkoxides for use in the presentinvention include calcium methoxide, calcium ethoxide, calciumn-propoxide, calcium i-propoxide, calcium n-butoxide, calciumsec-butoxide, calcium tert-butoxide and calcium t-amyloxide. Specificexamples include calcium dimethoxide, calcium diethoxide and calciumdi-i-propoxide. These calcium complexes may be used in combination oftwo or more kinds.

Examples of the gaseous calcium complexes include those obtained by heatvaporizing solid or liquid calcium complexes, those obtained by heatvaporizing calcium complex solutions, and mixtures thereof.

The gaseous calcium complex may be a vapor of one kind of the calciumcomplex or a mixed vapor of two or more kinds of the calcium complexes.The mixed vapor of two or more kinds of the calcium complexes may beobtained by mixing two or more kinds of the calcium complexes followedby vaporization, or by vaporizing two or more kinds of the calciumcomplexes followed by mixing.

Because the alkoxide is liable to be hydrolyzed, the use of the calciumalkoxide complex often results in problems such as decomposition beforethe vaporization to cause a lower yield and pipe clogging. Therefore, itis preferable that the alkoxide be stabilized in the form of an organicsolvent solution and then vaporized.

When the gaseous calcium complex is prepared by heat vaporizing acalcium complex solution, it may contain a vapor of one kind of thecalcium complex or a vapor of two or more kinds of the calciumcomplexes. When the gaseous calcium complex contains a vapor of two ormore kinds of the calcium complexes, it may be prepared by vaporizingtwo or more solutions containing different calcium complexes followed bymixing, or may be prepared by vaporizing a solution containing two ormore kinds of the calcium complexes.

The solvent used for the calcium complex solution is selected frommethyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol,tetrahydrofuran, dimethyl sulfoxide, dimethylformamide, hexane,cyclohexane, methylcyclohexane, dioxane, acetone, ethyl acetate, butylacetate, methyl isobutyryl ketone, diethyl ether, t-butyl methyl ether,acetyl acetone, diisobutyrylmethane and dipivaloylmethane. Thesesolvents can be used singly or in combination of two or more kinds. Theconcentration of the solution is not particularly limited.

In the present invention, an inert gas such as nitrogen or argon may beused as a carrier for the gaseous calcium complex.

Examples of the oxidizing substances for use in the present inventioninclude oxygen, mixed gases of oxygen with another gas, for example, aninert gas such as nitrogen or argon, in an arbitrary proportion, air,water and nitrous oxide. These oxidizing substances may be used singlyor in combination of two or more kinds.

Prior to combusting the calcium complex, the gaseous calcium complex andthe oxidizing substance may be preheated separately at temperatureslower than the decomposition temperature of the calcium complex. It isalso possible that the gaseous calcium complex and the oxidizingsubstance be mixed together and be preheated at temperatures lower thanthe decomposition temperature of the calcium complex. Furthermore, thegaseous calcium complex may be mixed with the oxidizing substance priorto the combustion. It is also possible that the gaseous calcium complexbe heated at temperatures not lower than the decomposition temperatureof the calcium complex and be released into the oxidizing substance toperform combustion simultaneously with the mixing with the oxidizingsubstance. When the calcium complex is in a liquid form or in a solutionform dissolved in an organic solvent, it may be mixed directly with theoxidizing substance.

The calcium complex and the oxidizing substance are preferably mixedtogether under conditions such that a completely mixed state isachieved.

It is preferable that the gaseous calcium complex and the oxidizingsubstance be combusted after mixed together. The combustion may bestarted by using an ignition source or by heating them at a temperaturenot lower than the ignition point.

Insufficient mixing will lead to incomplete combustion of the calciumcomplex, in which case unreacted materials such as carbides and waterremain and the fine particles are fused by prolonged reaction time. As aresult, the quality and particle diameter become unstable and theresulting particles generally have large diameters.

In the mixed gas of the oxidizing substance with the gaseous calciumcomplex or the gas generated by vaporization of the calcium complexsolution, it is preferable that the concentration of the calcium complexbe in the range of explosion. When the concentration is out of therange, the combustion is not stable. When the vapor pressure of thecalcium complex is low and the range of explosion is not reached, acombustion improver is preferably used. The combustion improver is notparticularly limited. For example, when using the calcium complexsolution, the solvent of the solution can be used as the combustionimprover.

When using the gaseous calcium complex prepared by heat vaporizing asolid or liquid calcium complex, the oxidizing substance is used in anoxygen molar amount 0.5 to 40 times, preferably 1 to 30 times, and morepreferably 1 to 20 times that required to completely oxidize the calciumcomplex. When using the gaseous calcium complex prepared by heatvaporizing a calcium complex solution, the oxidizing substance is usedin an oxygen molar amount 0.5 to 40 times, preferably 1 to 30 times, andmore preferably 1 to 20 times that required to completely oxidize thecalcium complex and the solvent. When the oxygen amount of the oxidizingsubstance used is too small, unreacted raw materials can cause theresulting calcium oxide fine particles to aggregate. When the oxygenamount is too large, the organic substance concentration becomes lowerthan the explosion limit and the combustion is not stable.

The combustion temperature in the present invention is preferably notlower than 400° C., particularly preferably in the range of 500 to 1500°C. When the combustion temperature is lower, unreacted raw materials orincompletely combusted organic components remain. When the combustiontemperature is too high, the apparatus lifetime is shortened andcontaminations occur due to deterioration of the apparatus materials.

The calcium oxide fine particles thus prepared range in median particlediameter (volume basis) from 1 to 200 nm.

More specifically, the aforesaid process for producing the calcium oxidefine particles may employ an apparatus as shown in FIG. 1.

FIG. 1 is a schematic diagram showing an embodiment of a productionapparatus used in the process for producing the calcium oxide fineparticles according to the present invention.

A solution 2 of β-diketone/calcium complex is quantitatively fed into aheating vaporizer 6 through a metering pump 4, and is vaporized here.The vapor containing the gaseous β-diketone/calcium complex vaporized inthe heating vaporizer 6 is quantitatively fed to a coaxial nozzle of aninlet of a tubular heating furnace 7 by quantitatively feeding a carriergas into the heating vaporizer 6 through the metering pump 4. Anoxidizing substance 1 (such as air) is quantitatively fed into apreheater 5 through a mass flow controller 3, and the preheatedoxidizing substance 1 is quantitatively fed to the coaxial nozzle of theinlet of the tubular heating furnace 7. The vaporized β-diketone/calciumcomplex and the oxidizing substance, which are fed through the coaxialnozzle, are mixed quickly and combusted (oxidation reaction) in thetubular heating furnace 7 to generate calcium oxide fine particles. Theresultant calcium oxide fine particles are collected by means of acollector 8.

The above-obtained calcium oxide fine particles generally containcalcium hydroxide (Ca(OH)₂) or calcium carbonate (CaCO₃) as impurities.Therefore, in order to convert these impurities into calcium oxide, abaking treatment is preferably carried out at 500 to 1,000° C. In thepresent invention, the treatment for converting Ca(OH)₂ and CaCO₃contained in the calcium oxide fine particles into CaO will be referredto as baking treatment.

Since the calcium oxide is extremely hygroscopic, a little water or thelike can work on calcium oxide (CaO) to form calcium hydroxide (Ca(OH)₂)or calcium carbonate (CaCO₃) during the above procedure. To prevent thecalcium oxide from containing such impurities, operations such as takingout the calcium oxide fine particles produced are preferably carried outin an atmosphere containing little or no water (for example, in a drynitrogen glove box), for example in an atmosphere having a water contentof not more than 10 ppm (by mol).

The calcium oxide dispersion liquid according to the present inventioncan be produced by dispersing the calcium oxide fine particles producedas described above in the aforesaid organic dispersion medium.

The calcium oxide fine particles prepared by the above method sometimescontain aggregated primary particles. Various methods are employable forpulverizing the aggregates, with examples including use of a bead millor a jet mill. For pulverization into nanoparticles, a bead mill ispreferably used. The smaller the bead size, the higher the pulverizationdispersion speed and the smaller the particle diameter achieved.Accordingly, the beads for use particularly preferably range in diameterfrom 5 to 200 μm, and particularly from 10 to 100 μm. From theviewpoints of abrasion resistance and minimization of impuritycontamination in calcium oxide, the beads are preferably made ofzirconia.

Addition of the organic dispersion medium in the pulverizing operationenables production of the dispersion liquid as soon as the pulverizationof the aggregates completes.

Specifically, production of the dispersion liquid simultaneously withthe bead mill pulverization may be performed by a process in which thecalcium oxide fine particles prepared by the above method, theaforementioned organic dispersion medium, and the beads are filled in acontainer and are stirred. In this process, the filling rate of thebeads is preferably in the range of 85 to 95%, and the calcium oxidefine particles are preferably used in an amount of 1 to 50% by massrelative to the total amount (100% by mass) of the calcium oxide fineparticles and the organic dispersion medium. The stirring time may beappropriately determined depending on the desired median particlediameter, and is generally about 10 minutes to 5 hours.

The pulverizing and dispersing operations are preferably carried out inan inert gas atmosphere in order to inhibit the calcium oxide fromabsorbing moisture of the atmosphere. Examples of the inert gasesinclude noble gases such as helium and argon, and nitrogen. The inertgas to be used preferably has a water content of not more than 10 ppm(by mol). When the inert gas has a high water content, the dispersionliquid absorbs moisture during the dispersion treatment, leading toproblems such as increase of calcium hydroxide, viscosity increase andcoloration.

Prior to producing the dispersion liquid simultaneously with the beadmill pulverization, the calcium oxide may be pre-dispersed in thedispersion liquid by means of ultrasonic wave, a planetary mixer or thelike.

The above-described process affords a dispersion liquid in which calciumoxide fine particles are homogeneously dispersed. In the presentinvention, the “dispersion liquid in which calcium oxide fine particlesare homogeneously dispersed” means that both fluidity and stabilitytests mentioned below of the dispersion liquid result in evaluation of“AA”.

EXAMPLES

The present invention will be described in more detail with reference tothe following examples, but it should be construed that the invention isin no way limited to the examples.

Analysis Methods

[Median Particle Diameter and Maximum Particle Diameter]

These particle diameters were measured using a particle sizedistribution analyzer (Microtrac UPA-150 model manufactured by NIKKISOCO., LTD).

Measurement condition: The dispersion liquid to be tested was diluted by100 times with the same solvent as used in the dispersion liquid.

[BET Surface Area]

Measuring apparatus: Chem BET-3000 manufactured by QUANTA CHROME CORP.

[Amounts of Calcium Hydroxide and Calcium Carbonate]

A thermobalance was used in this method.

Thermobalance: TG/DTA6200 model manufactured by Seiko Instruments Inc.

Measurement temperature range: 30 to 1,000° C.

Heating rate: 10° C./min

N₂ atmosphere: 200 ml/min

The amount of calcium hydroxide was determined by calculation fromweight reduction that had been caused by dehydration of calciumhydroxide occurring at about 300° C.

The amount of calcium carbonate was determined by calculation fromweight reduction that had been caused by decarboxylation of calciumcarbonate taking place at about 700° C.

Production Example 1

Calcium oxide fine particles were produced using an apparatus as shownin FIG. 1. Into a vaporizer 6 heated at 250° C., a mixed solution of 300g of Ca(DPM)₂ (manufactured by SHOWA DENKO K.K.) and 700 g of methanolwas fed at a flow rate of 4 mL/min and was vaporized. Air 1 was flowedinto a preheater 5 at a rate of 40 L/min and was heated to 250° C. Thegaseous Ca(DPM)₂ and the methanol, and the air were fed to a coaxialnozzle of an inlet of a tubular electric furnace 7. The combustiontemperature in the tubular electric furnace 7 was set at 950° C. Thecombustion time was 1 second. The oxygen molar amount in the air fed was1.5 times that required to completely oxidize the Ca(DPM)₂ and methanol.As a result, calcium oxide fine particles were collected in a collector8 in a yield of 90%. The calcium oxide fine particles had a medianparticle diameter of 30 nm. The fine particles are shown in a photographof FIG. 2.

The above-obtained fine particles contained calcium carbonate andcalcium hydroxide as impurities. In order to remove these impurities, anannealing treatment was carried out in an air atmosphere at 550° C. for5 hours, and further at 580° C. for 3 hours. The generated calcium oxideparticles had a BET surface area of 20 m²/g, which corresponds to anarithmetic mean particle diameter of 88 nm.

Thermogravimetric analysis was performed using the thermobalanceapparatus (TG/DTA6200 manufactured by Seiko Instruments Inc.) to measurethe calcium hydroxide and calcium carbonate contents. Both contents weredetermined to be less than 1% by mass, respectively.

Example 1

56 g of the calcium oxide particles obtained in Production Example 1were mixed with 504 g of 1-butanol having a water content of 9 ppm (bymass). The mixture was ultrasonicated for 1 hour to afford a homogeneousdispersion liquid. This dispersion liquid was treated in nitrogenatmosphere (water content: 8 ppm (by mol)) for 2 hours by use of a beadmill (UAM-015 manufactured by Kotobuki Engineering and ManufacturingCo., Ltd.) containing 50-μm zirconium oxide beads. As a result, adispersion liquid having a calcium oxide concentration of 10% by masswas obtained. The dispersion liquid was diluted by 100 times and wasanalyzed with the particle size distribution analyzer to determine theparticle size distribution, resulting in a median particle diameter of84 nm and a maximum particle diameter of 400 nm. The calcium hydroxidecontent and calcium carbonate content were determined to be less than 5%by mass and less than 1% by mass respectively.

Comparative Example 1

5 g of the calcium oxide particles obtained in Production Example 1 weremixed with 95 g of 1-butanol having a water content of 8 ppm (by mass).The mixture was ultrasonicated for 1 hour to afford a homogeneousdispersion liquid. The dispersion liquid was analyzed with the particlesize distribution analyzer (Microtrac UPA-150 manufactured by NIKKISOCO., LTD) to determine the particle size distribution, resulting in amedian particle diameter of 340 nm and a maximum particle diameter of1,370 nm.

Examples 2 to 13

Examples 2 to 13 were carried out in which the kind of the dispersionmedium and the calcium oxide concentration were changed.

Calcium oxide particles having a BET surface area of 18 m²/g (whichcorresponds to an arithmetic mean particle diameter of 100 nm) wereobtained by the same method as in Production Example 1 except that thesecond annealing treatment was carried out at 700° C. for 1 hour. Thecalcium oxide particles were mixed with 312 g of the dispersion medium(media) shown in Table 1, so as to achieve a calcium oxide concentrationshown in Table 1. The mixture was ultrasonicated for 1 hour to afford ahomogeneous dispersion liquid. All the (mixed) dispersion media used inthese examples had a water content of not more than 1,000 ppm. Thedispersion liquid was treated in nitrogen atmosphere (water content: 8ppm (by mol)) for 2 hours by use of a bead mill containing 50-μmzirconium oxide beads. As a result, a calcium oxide dispersion liquidhaving a concentration shown in Table 1 was obtained in each example.After the dispersion liquid had been diluted by 100 times, the particlesize distribution was measured with the particle size distributionanalyzer to determine the median particle diameter and the maximumparticle diameter. In each example, the calcium hydroxide content andthe calcium carbonate content were determined to be less than 5% by massand less than 1% by mass. respectively.

The dispersion medium kinds, the calcium oxide concentrations, and theresults are shown in Table 1.

The dispersion liquid of Example 2 was allowed to stand at roomtemperature for 7 days, and its particle size distribution was measuredagain. The measurement resulted in a median particle diameter of 90 nmand a maximum particle diameter of 400 nm, which proved that theobtained dispersion liquid was extremely stable.

The dispersion liquids of Examples 1 to 13 had a smaller median particlediameter and a smaller maximum particle diameter than those obtained inComparative Example 1. This result probably shows that the secondaryaggregates were pulverized by the bead mill.

Further, the results provide that the dispersion treatment in nitrogenatmosphere inhibits moisture absorption of the calcium oxide to asatisfactory level.

Example 14

A calcium oxide dispersion liquid was produced in the same manner as inExample 13, except that 0.9 g of diethanol amine as dispersion medium-2and 3.7 g of GL-100 (available from Asahi Denka Co., Ltd.) as dispersantwere added to the dispersion liquid prior to the bead mill treatment.The median particle diameter and the maximum particle diameter were 60nm and 240 nm, respectively. The dispersion liquid was allowed to standat room temperature for 7 days, and its particle size distribution wasmeasured again. The measurement resulted in the same results, i.e., amedian particle diameter of 60 nm and a maximum particle diameter of 240nm, which proved that the obtained dispersion liquid was extremelystable. TABLE 1 Dispersion Dispersion Median particle medium-1 Medium-2diameter Calcium oxide Kind and Kind and (Maximum particle concentrationconcentration concentration diameter) Fluidity Stability Example 1 10%by mass 1-Butanol None 84 nm AA AA 100% by mass (400 nm) Comparative 5%by mass 1-Butanol None 340 nm AA CC Example 1 100% by mass (1,370 nm)Example 2 15% by mass 1-Butanol None 100 nm AA AA 100% by mass (250 nm)Example 3 15% by mass 1-Hexanol None 80 nm AA AA 100% by mass (350 nm)Example 4 20% by mass Xylene Monoethanolamine 85 nm AA AA 99.5% by mass0.5% by mass (400 nm) Example 5 20% by mass Toluene 1-Hexanol 75 nm AAAA 99.5% by mass 0.5% by mass (300 nm) Example 6 20% by massAcetonitrile None 80 nm AA AA 100% by mass (360 nm) Example 7 30% bymass Acetonitrile 1-Butanol 85 nm AA AA 99.9% by mass 0.1% by mass (350nm) Example 8 30% by mass Acetonitrile 1-Hexanol 75 nm AA AA 99.9% bymass 0.1% by mass (300 nm) Example 9 25% by mass DMF 1-Hexanol 85 nm AAAA 99.9% by mass 0.1% by mass (400 nm) Example 10 30% by mass DMAC1-Hexanol 75 nm AA AA 99.9% by mass 0.1% by mass (300 nm) Example 11 30%by mass Butyl acetate 1-Hexanol 75 nm AA AA 99.9% by mass 0.1% by mass(300 nm) Example 12 20% by mass Diglyme Monoethanolamine 85 nm AA AA99.9% by mass 0.1% by mass (390 nm) Example 13 30% by mass PGME None 83nm AA AA 100.0% by mass (240 nm) Example 14 30% by mass PGMEDiethanolamine 60 nm AA AA 99.6% by mass 0.4% by mass (240 nm)

“Calcium oxide concentration” shows calcium oxide concentrations in thedispersion liquids.

“Dispersion medium-1” shows kinds and concentrations (concentration ofDispersion medium-1 in the dispersion medium) of Dispersion medium-1.

“Dispersion medium-2” shows kinds and concentrations (concentration ofDispersion medium-2 in the dispersion medium) of Dispersion medium-2.

Abbreviations of the dispersion media:

DMF=N,N-dimethylformamide

DMAC=N,N-dimethylacetamide

Diglyme=diethylene glycol dimethyl ether

PGME=1-methoxy-2-propanol (propylene glycol monomethyl ether)

“Median particle diameter” shows median particle diameters (volumebasis) of calcium oxide in the dispersion liquids. The numbers inparentheses show maximum particle diameters.

“Fluidity” shows fluidities of the dispersion liquids. A 180-ml clearglass container (50 mm in diameter) having a cap was filled with 50 mlof the dispersion liquid. The container was then quickly tilted 90degrees, and the fluidity of the liquid was observed. This measurementwas carried out at room temperature.

AA . . . The dispersion liquid flowed as soon as the container wastilted.

BB . . . The dispersion liquid flowed slowly after the container hadbeen tilted.

CC . . . The dispersion liquid did not flow even after the container hadbeen tilted.

“Stability”: A 180-ml clear glass container (50 mm in diameter) having acap was filled with 50 ml of the dispersion liquid. The container waskept at room temperature for 1 week, and the dispersion liquid wasobserved.

AA . . . No change was observed.

BB . . . A clear supernatant was observed.

CC . . . Precipitation was observed.

1. A calcium oxide dispersion liquid comprising: calcium oxide fineparticles having a median particle diameter (volume basis) of 1 to 200nm and a maximum particle diameter of 10 to 1,000 μm; and an organicdispersion medium.
 2. The calcium oxide dispersion liquid according toclaim 1, which has a calcium oxide concentration of 10 to 50% by mass.3. The calcium oxide dispersion liquid according to claim 1, which isobtained by using the organic dispersion medium which has a watercontent of less than 1,000 ppm (by mass) as a raw material.
 4. Thecalcium oxide dispersion liquid according to claim 1, wherein thecalcium oxide fine particles are obtained by vaporizing a calciumcomplex, and then oxidizing the resultant gaseous calcium complex in gasphase.
 5. The calcium oxide dispersion liquid according to claim 1,wherein the calcium oxide fine particles are obtained by vaporizing acalcium complex, oxidizing the resultant gaseous calcium complex in gasphase to obtain calcium oxide fine particles, and then subjecting thefine particles to baking treatment.
 6. The calcium oxide dispersionliquid according to claim, wherein the calcium complex is a complex ofcalcium and a β-diketone compound.
 7. The calcium oxide dispersionliquid according to claim 1, wherein the calcium oxide fine particleshave a calcium hydroxide content of less than 5% by mass and a calciumcarbonate content of less than 1% by mass.
 8. The calcium oxidedispersion liquid according to claim 1, wherein the organic dispersionmedium is at least one medium selected from the group consisting ofalcohol, nitrile compound, amide compound and polyol derivative.
 9. Thecalcium oxide dispersion liquid according to claim 8, wherein thealcohol has 3 or more carbon atoms.
 10. The calcium oxide dispersionliquid according to claim 8, wherein the organic dispersion medium isdiol derivative.
 11. The calcium oxide dispersion liquid according toclaim 1, wherein the organic dispersion medium is at least one mediumselected from the group consisting of acetonitrile, 1-butanol, 1-hexanoland 1-methoxy-2-propanol.
 12. The calcium oxide dispersion liquidaccording to claim 1, wherein the organic dispersion medium is a mixeddispersion medium.
 13. The calcium oxide dispersion liquid according toclaim 12, wherein the organic dispersion medium is at least one mediumselected from the group consisting of a nitrile compound/alcohol mixeddispersion medium, an aromatic compound/alcohol mixed dispersion medium,an aromatic compound/amine compound mixed dispersion medium, anester/alcohol mixed dispersion medium, an amide compound/alcohol mixeddispersion medium, an aromatic compound/nitrile compound mixeddispersion medium and a polyol derivative/amine compound mixeddispersion medium.
 14. The calcium oxide dispersion liquid according toclaim 12, wherein the mixed dispersion medium is at least one mediumselected from the group consisting of a toluene/alcohol mixed dispersionmedium, a butyl acetate/alcohol mixed dispersion medium, anN,N-dimethylacetamide/alcohol mixed dispersion medium, a diethyleneglycol dimethyl ether/monoethanolamine mixed dispersion medium, adiethylene glycol dimethyl ether/diethanolamine mixed dispersion mediumand a diethylene glycol dimethyl ether/triethanolamine mixed dispersionmedium.
 15. The calcium oxide dispersion liquid according to claim 1,which contains a dispersant.
 16. The calcium oxide dispersion liquidaccording to claim 15, wherein the dispersant is at least one compoundselected from nonionic surfactants.
 17. The calcium oxide dispersionliquid according to claim 16, wherein the nonionic surfactant has ahydroxyl group.
 18. The calcium oxide dispersion liquid according toclaim 16, wherein the nonionic surfactant is an adduct of glycerin withpolypropylene oxide.
 19. The calcium oxide dispersion liquid accordingto claim 1, wherein the organic dispersion medium has a viscosity of notmore than 3.0 mPa·s (20° C.).
 20. A process for producing the calciumoxide dispersion liquid according to claim 1, which comprises the stepsof: filling calcium oxide fine particles, an organic dispersion medium,and beads having a diameter of 5 to 200 μm into a container; andstirring these materials.
 21. The process according to claim 20, whereinthe stirring is carried out in an atmosphere of an inert gas having awater content of not more than 10 ppm (by mol).
 22. The processaccording to claim 20, wherein the organic dispersion medium to befilled in the container has a water content of less than 1,000 ppm (bymass).
 23. The calcium oxide dispersion liquid according to claim 5,wherein the calcium complex is a complex of calcium and a β-diketonecompound.